1. Technical Field of the Invention
This invention relates to a transmission system for detecting measurement data (i.e., temperature data) of a rotating body and for transmitting the measurement data from the rotating body to a stationary receiver via a contactless transmission path, and is particularly concerned with the structure of a printed circuit board assembly for a rotary transmitter in the measurement data rotary transmission system.
2. Description of the Prior Art
In the synthetic fiber industry, metal rollers generally called roll heaters are used which are heated by an induction heater and rotated by a motor at high speeds for drawing and heat-setting yarns. In order to produce yarns of good quality, the surface temperature of the roll heater should be controlled to be at an optimum for the yarn processing. It is necessary to accurately detect the surface temperature of the metal roller and to transmit the measurement data to a temperature control device for the roller. One known system includes a temperature sensor embedded in the metal roller which produces an output signal which is delivered externally, via a brush and slip ring, to a fixed stationary heater control device comprising a central processing unit. However, the latter arrangement does not enable the heater control device to pick up the output signal with stability and precision over a long period of time.
Since such a system fails to meet practical requirements, a contactless signal transmission system has been employed in the art. In the contactless system, the rotating body has a transmitter for converting a temperature sensor output to a predetermined signal form and for transmitting the latter to a stationary receiver via a contactless transmission path. Various contactless systems comprise such a transmitter.
In one system, a temperature sensor comprises a thermoresistor, whose resistance varies as a function of temperature. A Wien bridge detects the resistance of the resistor and converts it to a frequency signal, which is then transmitted through a rotary transformer to a stationary receiver.
In another contactless transmission system, a signal indicative of the resistance of the temperature sensor is amplified and frequency-modulated by a modulator and is transmitted to the stationary receiver via a transmission circuit and an aerial.
In yet another contactless transmission system, an output signal from the temperature sensor is converted to a corresponding frequency signal which is then converted by an electrooptical converter to a light signal that is optically transmitted from a light-emitting element to a photosensitive element associated with the stationary receiver.
A latter type of temperature signal transmission apparatus for transmitting light signals is shown in a schematic block circuit diagram in FIG. 1, and a roll heater utilizing such a temperature signal transmission apparatus is schematically illustrated in FIG. 2.
In the apparatus shown in FIG. 1, a temperature signal transmitter 1 is mounted on a roller of a roll heater and has a temperature sensor 2 which produces an output signal indicative of temperature. The output signal delivered through a voltage conversion circuit 3, an amplification circuit 4, a voltage-to-frequency conversion circuit 5, and an energization circuit 6 to a signal transmitter or a light-emitting element 7 which produces a light output signal. The temperature signal transmitter 1 is supplied with electrical power from a stationary receiver 11 through a secondary winding 8 or a rotary transformer serving as a power supply, a rectification circuit 9, and a constant-voltage supply circuit 10.
The stationary receiver 11 comprises a photosensitive element 12 disposed on the optical axis of the light-emitting element 7 and receives the light signal therefrom, and a conversion circuit 13 converts the light signal to an electric signal, which is delivered to a central processing unit 14 serving as a heater control device. The rotary transformer has a stationary primary winding 8'.
A roll heater equipped with the temperature signal transmission apparatus thus constructed is shown in FIG. 2. The roll heater comprises a metal roller 18 mounted on one end of a rotational shaft 16 of a drive motor 15 and arranged to be heated by a fixed induction heater coil 17, the metal roller 18 having the temperature sensor 2 embedded therein. The other end of the rotational shaft 16 supports the transmitter 1 which is electrically connected to the temperature sensor 2 by means of a wire 19 extending through a central axial bore in the rotational shaft 16. The receiver 11 and the primary winding 8' of the rotary transformer are supported on a frame projecting laterally from a casing of the motor 15. The temperature sensor may comprise thermally sensitive elements such as a thermistor or a thermocouple, as well a thermoresistor as mentioned above.
The circuits 3 to 6 of the transmission apparatus as shown in FIG. 1 are normally constructed as printed circuits which include various electronic components such as ICs, miniature capacitors, resistors, transistors and diodes mounted on printed circuit boards. These electronic parts are soldered to the boards via thin wires, and hence are mechanically unstable. The wires are prone to break under undue external forces applied accidentally, resulting in damage to the mounted parts. Accordingly, the printed circuits should be handled with care. Since the roll heater is rotated at high speeds while in operation, the electronic components assembled and mounted on the roller are subjected to considerable centrifugal forces. Therefore, there has been much concern about how to safeguard against centrifugal forces imposed on the electronic components of the transmitter.
Various attempts have been made to provide assembly structures for electronic components to be mounted on the roller. However, none of the prior proposals have met practical requirements, since the electronic components tend to give way under centrifugal forces which result when the roller revolves at high speeds. While efforts have been made to increase the mechanical strength by encasing the printed circuits in plastic material, such encasement of the parts is disadvantageous because the printed circuits cannot be inspected and the individual components cannot be replaced. Therefore, there is a need for a system which overcomes all of the problems of prior systems discussed above.